Diets for laboratory culture of Daphnia usually consist of unicellular algae. Because intensive culture of unicellular algae is expensive and labour intensive, partial replacement of algae by yeast could reduce the cost for laboratory culture of Daphnia. In order to determine the effect of food quality on phototactic behaviour of D. magna we tested whether the substitution of a part of unicellular algae (Scenedesmus acutus) by fresh bakers yeast (Saccharomyces cerevisiae) has a significant effect on phototactic behaviour and life history traits of the positive phototactic clone C134. In addition we examined whether an additional supply of ciliates to yeast diets improves the performance of Daphnia compared to a diet solely consisting of yeast. Animals fed with a diet containing less than 25 % algae showed a similar phototactic behaviour as animals fed with a diet that contained 100 % algae. The results of the cohort life table experiment indicate that diets for culturing Daphnia should contain at least 25 % unicellular algae to guarantee a good physiological condition of the animals. Addition of ciliates to yeast diets resulted in a positive effect on the physiological condition of the animals but did not influence the phototactic behaviour.